1. Field of the Invention
The present disclosure pertains to prevention and treatment of insect infestation in plants. More specifically, this disclosure relates to the use of extracts or chemicals from Ginkgo or their synthetic counterparts to prevent or to treat insect infestation or invasion.
2. Description of Related Art
The codling moth, Cydia pomonella, is a major insect pest for apple trees. If not controlled, it may cause an annual loss of more than 40 billion U.S. dollars globally. The grower has very limited options to control of this insect because during the invasive stage, the neonate larva burrows into the fruit shortly after hatching from eggs where it stays until its development is completed. Additionally, in areas where codling moth have partial third generation, the neonates typically attempt to infest apples during harvest when the use of insecticides is banned. Broad-spectrum organophosphate neurotoxin and azinphos-methyl remain the major control measure against codling moth. However, these insecticides need to be applied in excessive amounts of (e.g., 1.7 kilograms per hectare) because some codling moths have become resistant to azinphos-methyl over the years. Moreover, this pesticide has been linked to health problems of agricultural workers which raise serious concerns from U.S. Environmental Protection Agency (EPA). In fact, this insecticide has been banned in European Union and is to be phased out in some other countries.
Other insecticides have been developed based on natural pathogens of codling moth, such as bacteria or viruses. However, such insecticides are expensive and are not very effective because damages are usually done before the larvae are killed by the insecticides. Other chemical agents also have disadvantages. For instance, pheromones based on behavioral manipulation such as mating disruption or attract-and-kill have been reported. However, such measures do not resolve problems caused by migration of moths from adjacent areas (Wolfgang, 1989) or insecticide resistance (Poullot et al., 2001).
Ginkgo trees have long been known to possess exceptional resistance to pests and pathogens (Major, 1967). However, the underlying mechanisms of Ginkgo's natural resistance have not been studied extensively. Two studies have been reported showing deterrent effects of extracts from Ginkgo foliage on feeding by two cabbage insect pests, Pieris brassicae and Pieris rapae, respectively (Matsumoto and Sei, 1987; Fu-shun et al., 1990). Indirect methods used in these studies leave an open question as to whether feeding was actually inhibited, or Ginkgo extracts merely acted as a constipation factor. Effects of anacardic acids on insect development and feeding were studied in only one insect species, the Colorado potato beetle (Schultz et al., 2006). Despite the wealth of data about diversity of flavonoids in plants, few of these compounds have been tested against insects and even less is known about their effects on insect feeding (Simmonds, 2001, 2003). There is evidence that some flavonoids have deterrent and anti-feeding effect on the crucifer pest Mamestra configurata (Onyilagha et al., 2004). In a single paper, researchers were focused on insecticidal properties of these compounds in a hemipteran (Nilaparvata lugens) (Ahn et al., 1997). However, the reactions of codling moth larvae to flavonoids have not been studied. The effects of Ginkgo trilactone terpenes on insect feeding have not been studied.